International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Concrete with Supplementary Cementitious Materials 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Ghent University Academic Bibliography PARTICLE SIZE DISTRIBUTION AND SPECIFIC SURFACE AREA OF SCM'S COMPARED THROUGH EXPERIMENTAL TECHNIQUES Natalia M. Alderete(1,2), Yury A. Villagrán Zaccardi(2), Gabriela S. Coelho Dos Santos(2), Nele De Belie(1) (1) Magnel Laboratory for Concrete Research, Department of Structural Engineering, Faculty of Engineering and Architecture, Ghent University, Belgium (2) LEMIT Laboratory for Multidisciplinary Training in Technological Research, La Plata, Argentina Abstract Supplementary cementitious materials (SCMs) are mainly used to produce a green concrete. To reach that goal effectively, it is highly important to adequately characterize the SCMs. It is well known that particle size distribution (PSD) and fineness of SCMs have a great influence on concrete properties. Traditionally, cement fineness has been assessed by the specific surface area (SSA) through the Blaine method (BM). However, the BM has the simplification of considering ideal spherical shape particles. The BET theory has also been used to calculate SSA, however, also some assumptions may lead to inaccuracy in the calculations. Both PSD and SSA can be evaluated through Laser Diffractometry (LD), but this technique also considers ideal spherical particles as a simplification. Regardless of the mentioned drawbacks, these techniques provide useful information to characterize SCMs provided that the limitations are considered. In this paper, Ground Granulated Blast Furnace Slag (GGBFS), Natural Pozzolan (NP) and Limestone Powder (LP) are tested using the BM, LD, and nitrogen adsorption. Particle texture and shape are assessed through petrography and scanning electron microscope (SEM). Results from BM, BET and LD are compared, analysing the possible effects of particle shape and texture. 1. Introduction Fineness from supplementary cementitious materials (SCMs) is generally evaluated as an influencing parameter on the properties of concrete. However, the assessment of fineness through different experimental techniques is not usually considered adequately, and some limitations are disregarded leading to an incorrect interpretation of results. Generally, standard methods used to assess physical properties of cement have been straightforwardly applied for SCMs without any modification. However, the same techniques may not always be applicable due to differences in shape and size of SCMs. 61 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Concrete with Supplementary Cementitious Materials 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark For the determination of the specific surface area (SSA), the Blaine method (BM) has been commonly used for cement [1- 3]. BM is a rather empirical method particularly designed for cements, and therefore its application for SCMs requires some adaptations. For example, a different plunger has been proposed by [4] to avoid removing it. This modified plunger was used by [5] to test silica fume with unsatisfactory results as a well compacted bed could not be achieved. Alternatively to the BM, laser difractometry (LD) is a quick technique that uses the optical properties of the powder to evaluate both its SSA and its particle size distribution (PSD). LD has been fairly well described in [6-8], where the importance of the dispersion conditioning and the correct selection of the optical parameters are highlighted. Another technique for SSA determination is the use of the Brunauer, Emmett, and Teller (BET) theory [9] which is based on the amount of gas adsorbed on a monomolecular layer on the surface. This has the evident advantage of not assuming a specific particle shape; however, some simplified assumptions, as the existence of a homogenous covering layer [10] may not lead to the actual SSA value. In this study, fineness of Ground Granulated Blast Furnace Slag (GGBFS), Natural Pozzolan (NP) and Limestone Powder (LP) is measured and compared with the three techniques. Guidelines in ASTM C204-07 [11] for the application of the Blaine method to materials other than cement are followed. Some recommendations in addition to those in the literature are proposed to obtain reliable results from LD. Finally, the results are compared with characterization through petrography and scanning electron microscopy (SEM), with assessment of particle shape and texture and their influence on the values obtained and the theoretical considerations of each method. 2. Materials and methods 2.1. Materials This study includes analysis of ground granulated blast furnace slag (GGBFS), natural pozzolan from volcanic origin (NP) and limestone powder (LP).Both GGBFS and NP were first dried in oven for 24 h, and then ground in a laboratory ball mill for cement, with the aid of cylpebs. The grinding process was carried out for 1.5 h for the GGBFS and 2.0 h for the NP. LP was also processed in an industrial ball mill. The chemical composition of the materials is shown in Table 1.The chemical analysis was performed by X-ray fluorescence and the density was determined according to ASTM C188-15 [12]. 62 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Concrete with Supplementary Cementitious Materials 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark Table 1: Chemical compositions of GGBFS, NP and LP. wt (%) GGBFS NP LP CaO 36.16 1.34 48.85 SiO2 28.89 62.53 8.15 MgO 12.14 1.13 1.41 Al2O3 8.62 10.76 1.28 Na2O 1.91 5.66 1.25 SO3 1.85 0.34 0.05 Fe2O3 0.95 1.81 0.88 TiO2 0.46 0.09 - K2O 0.43 3.67 0.28 MnO 0.43 0.06 0.04 LOI nd- nd- 37.29 Density (g/cm3) 2.92 2.41 2.71 nd = not determined 2.2. Methods 2.2.1. Blaine method The BM test was performed according to ASTM C204-07 [11], where the special consideration for materials other than cement intends to consider the possible differences in density, porosity or shape in relation to a standard reference material. 2.2.2. Laser diffraction The particle size distribution by means of LD was determined using a particle analyser Malvern Mastersizer 2000 E, wet unit Hydro 2000SM (A). Isopropanol (IPA) was used as a dispersant for the three SCMs. For the refractive index (m = n+ ik), different values of refraction index (n) and absorption coefficient (k) were used for each SCM, according to the data found in literature [6-8]. Those combinations of values which had the best fit and less weight residual were selected. Selected values of n and k are presented in Table 2. As described in [6] duration of dispersion, ultrasonication frequency, stirrer rate, measurement time and obscuration levels were first optimized in order to obtain reliable results for each of the SCMs. Particular attention was paid to the dispersion procedure since failure in this step leads directly to erroneous results. The selected procedure consisted of 5 minutes of ultrasonic bath (35 kHz, 320 W), 1700 rpm for the stirrer rate, 20 s of measuring time and 11.5 ± 0.5% of obscuration level. After the de-agglomeration of the particles was finished, a syringe was used to collect the sample and place it inside the diffractometer. The same procedure (stirring speed, sonification time and frequency, sample and background measurement time, obscuration level) was applied for all the SCMs changing only the values of n and k for each particular case. 63 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Concrete with Supplementary Cementitious Materials 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark Table 2: Selected optical parameters of the SCMs. GGBFS NP LP n 1.62 1.49 1.57 k 0.1 0.1 0.05 2.2.3. BET method For quantitative analysis, adsorption and desorption curves using nitrogen at 77 K were determined with a Micromeritics Asap 2020. Before measurement, samples were dried at 105°C and kept in a desiccator until testing. The BET adsorption theory was used for the determination of surface area, using the corresponding values of the relative pressure between 5-35% of the adsorption curve. 2.2.4. Petrographic characterization 2.2.4.1 Petrographic microscope Petrographic characterization of the SCMs was done in accordance to ASTM C295 [13]. The equipment used is an Olympus BH2-UMA petrographic microscope. This instrument includes an Infinity 1-3C digital camera of13.1 megapixels. Image processing was done with Infinity Analyze 5.0 software. 2.2.4.2 Scanning electron microscope (SEM) The SEM allows analysing materials morphology with micrometric detail. All the information registered can be translated into external morphology and materials orientation [14]. A SEM 505 Philips was used to perform the characterization. 3. Results 3.1. Blaine method Some difficulties for achieving an adequate bed height with a given porosity (İ) have been found when testing SCMs [5]. The ASTM C204-07 addresses this problem by calculating a constant (b) appropriate for each sample, which is obtained by plotting the values of ¥(İ3.T) versus İ and determining the y-intercept by linear regression. For the calculation of the value of b, a minimum of 12 determinations have to be made. Four samples of each SCM were tested at four different İ values, and the b characteristic value of each SCM was calculated. The results of the SSA and the bed porosity range used for each material are shown in Table 3. 64 International RILEM Conference on Materials, Systems and Structures in Civil Engineering Conference segment on Concrete with Supplementary Cementitious Materials 22-24 August 2016, Technical University of Denmark, Lyngby, Denmark Table 3: Blaine SSA and bed porosity range of the SCMs GGBFS NP LP Porosity values 0.53,0.55,0.57,0.59 0.53,0.55,0.57,0.59 0.47,0.49,0.51,0.53 Surface area (m2/kg) 341±4 858±12 646±5 3.2.